The present disclosure relates to interior permanent magnet (or xe2x80x9cIPMxe2x80x9d) machines such as, for example, an IPM motor. IPM machines have been used in various applications in the past, but the use of such machines in applications requiring a high degree of torque from a relatively small machine or low-noise has been limited by certain characteristics of IPM machines.
For example, because IPM machines utilize a rotor that contains a number of interior permanent magnets, there is a tendency for magnetic flux produced by the magnets to circulate between two adjacent magnets. This intra-magnet flux circulation tends to reduce the overall torque output of the machine because the magnetic flux that circulates between the magnets is not readily available for torque production. In addition to reducing the overall torque output of the machine, this intra-magnet flux circulation also tends to decrease the overall efficiency of the machine.
Further, IPM motors because of their use of discretely positioned interior permanent magnets tend to have a degree of unwanted torque ripple or torque variation often known as xe2x80x9ccogging torque.xe2x80x9d Such cogging torque can produce unwanted noise and/or vibrations and can reduce the overall efficiency of the machine.
A further characteristic of IPM machines that potentially limits the torque output and efficiency of such machines is the ability to get current into the windings of such machines. The ability to get current into the machine is an important factor in producing torque and having an efficient machine as the torque out of the machine will correspond closely to the amount of current that is put into the phase windings and the speed at which the current its placed in the phase windings will impact the efficiency of the machines. Typically, IPM motors have had a construction that generally results in the phase windings of such machines having a relatively high inductance. This relatively high inductance has tended to limit the ability to get current in to the windings of such machines.
The present disclosure described several embodiments of IPM machines that are designed to address the described, and other, limiting characteristics of IPM machines to provide an improved IPM machine that has, for example, a relatively high torque output, high efficiency and low cogging torque.
In accordance with one exemplary embodiment constructed in accordance with certain teachings of the present disclosure a rotor for an interior permanent magnet machine is provided that includes a permanent magnet positioned within in the interior of the rotor, and at least two impedance reduction slits associated with the permanent magnet.
In accordance with another exemplary embodiment constructed in accordance with certain teachings of the present disclosure an interior permanent magnet machine is provided that includes a stator defining a number of stator poles and stator teeth, the stator teeth defining slot openings therebetween; a rotor; a plurality of permanent magnets positioned within the interior of the rotor, and at least two impedance reduction slits associated with each permanent magnet, each impedance reduction slit comprising an air gap positioned radially outward of its associated permanent magnet, wherein each impedance reduction slit is positioned such that at least a portion of the slit is within a defined region wherein: (i) an imaginary line radially extending from the center of the rotor through the midpoint of the defined region defines an angle with respect to an imaginary line radially extending from the center of the rotor through the midpoint of the permanent magnet associated with the slit, wherein the defined angle is approximately equal to the absolute value of [360xc2x0/R xe2x88x92360xc2x0/S] where R is the number of permanent magnets and S is the number of stator poles; and (ii) the angular width of the defined region is approximately equal to the angular width of the slot opening between adjacent stator teeth.
In accordance with yet another exemplary embodiment constructed in accordance with certain teachings of the present disclosure a rotor for an interior permanent magnet machine is provided that includes at least two permanent magnets positioned within in the interior of the rotor, at least two impedance reduction slits associated with the permanent magnet, each impedance reduction slit being positioned radially outward of the permanent magnets and a low permeability region positioned between the ends of the permanent magnets.
In accordance with yet another exemplary embodiment constructed in accordance with certain teachings of the present disclosure a interior permanent magnet machine is provided that includes a stator, at least one phase winding positioned within the stator; a plurality of permanent magnets positioned within the interior of the rotor; and means positioned within the rotor for reducing the impedance of the phase windings.